The occurrence of oil crisis makes people to start emphasizing the subjects of energy saving and protection of earth's resources. Automobiles are the major vehicles for transportation. They are also the main source of pollution because of the exhaust and the energy consumption. Thereby, lightweight of car construction has become a significant direction for improvement. By thinning the material, the weight of cars is lowered, and hence reducing the fuel consumption and improving exhaust emission. The materials of current commercial wheels mainly include steel or aluminum alloy; some also include magnesium or titanium alloy. The manufacturing methods include casting, forging, and welding. The related technologies for steel or aluminum-alloy wheels are disclosed in patent publication numbers TW 1313207, TW 1225808, and CN 1291557A. They all form a rim by welding the junction of two edges of a rolled metal sheet (steel sheet) or aluminum sheet using the traditional welding technology. Although the technologies in the above patents achieve the purpose of manufacturing steel or aluminum-alloy wheels, their main emphasis is on reducing the manufacturing costs of wheels, instead of reducing and thinning materials for reducing the weight of automobiles. Accordingly, considering the purposes of lightweight automobile wheels, reducing fuel consumption, and then improving exhaust emission, the above designs are apparently not ideal.
The crux hindering traditional car wheels to be even more lightweight is because steel wheels are usually formed by two-piece, namely, the rim and the disk, welding. The grades of the materials of the rims and the disks adopted by the technology according to the prior art, the breakthrough of the welding technology according to the prior art, and how to match the two have become the critical points. For example, the material used in the steel rims of all terrain vehicles (ATV) is 440 MPa steel grade and the material for the disks is 590 MPa steel grade. Besides, flash welding is adopted for fabricating rims of traditional cars. Flash welding is a fast and high-resistor heat welding method. The formation of rims is complicated and rigorous with five formation welds. When applied to steel grades under 440 MPa, flash welding is decent in the forming application. Nonetheless, as applied to steel grades of higher strength such the steel grades above 590 Mpa, after flash welding, the hardness of the welds and the heat-affected zone is raised abnormally, leading to cracks in the subsequent formation processes of the rims and lowering the yield significantly. For another example, in the tradition metal active gas (MAG) arc welding, which is also known as CO2 welding, due to its characteristics of continuous wire feeding and spatter displacement during welding, the arc is relatively unstable. Consequently, the hardness of the welds or the heat-affected zone is not uniform. Sometimes, soft regions may appear; sometimes, abnormal hardening may occur. Thereby, as applied to the development of wheels with higher strength, cracks usually occur on the formed rim roll. Alternatively, in the radial test after the rims and the disk are assembled and welded to form a wheel, cracks usually occur. Accordingly, the fatigue lifetime is too low to pass the test.
Limited by the welding technology, the material of rim adopted by the leading domestic manufacturer of car wheels currently is as high as 440 MPa steel grade only. The materials of the rims and the disks used by the greatest domestic manufacturer of ATV wheels are still 440 MPa steel grade, unable to be raised to advanced high-strength steel grades. Moreover, wheel manufacturers weld rims and disks to produce wheels. In general, they use the traditional MAG arc welding. Because the MAG welding has greater heat input, the heat-affected zone is broader. Thereby, the strength of the welded parts degrades, and their fatigue lifetime is also shorter. Besides, the spatters are more, which affects the protection effects to some degree; the quality of welds is inferior, and the grinding operations and costs in post processes are increased. Thereby, how to improve the drawbacks in the manufacturing methods of wheels (steel wheels) according to the prior art has become an important direction of development in the industry.
Accordingly, the present invention provides a manufacturing method for advanced high-strength steel wheel and the jig device thereof, which feature external simplicity in construction, convenience in assembly, and convenience in stacking and positioning.